Studies on the biochemical effects of drugs in animals and man using mass spectral methodology are being pursued in order to relate pharmacological action to molecular events and clinical efficacy. Work in progress includes synthesis of stable isotope labeled compounds for kinetic studies in man of neurotransmitters, and the effects of various drugs upon the synthesis and release of catecholamines. Drug manipulation of melatonin and 6-hydroxymelatonin levels are being measured to indicate beta-adrenergic receptor activity. Tricyclic antidepressants are being quantitated from patients by mass spectral measurements in order to establish therapeutic and predictive indices. Pharmacokinetic studies of phencyclidine in monkeys are in progress.